mikolalysenko / simplicial-complex-boundary

Extracts the boundary of a simplicial complex

simplicial-complex-boundary

Extracts the boundary of a simplicial complex.

Example

var boundary = require('simplicial-complex-boundary')

var cells = [
  [0,1,2],
  [1,2,3]
]

console.log(boundary(cells))

Output:

[ [ 0, 1 ], [ 0, 2 ], [ 1, 3 ], [ 2, 3 ] ]

Install

npm i simplicial-complex-boundary

API

var bnd = require('simplicial-complex-boundary')(cells)

Computes the boundary of a simplicial complex

• cells are the cells of a simplicial complex

Returns The boundary of the simplicial complex (in the Z/2 homology sense)

License

(c) 2015 Mikola Lysenko. MIT License

simplicial-complex-boundary's Issues

Example in readme broken

The example given in the readme file does not work:

var boundary = require('simplicial-complex-boundary')
var cells = [
  [0,1,2],
  [1,2,3]
]
boundary(cells)

results in

[ [ 0, 1 ], [ 2, 0 ], [ 1, 2 ], [ 1, 2 ], [ 3, 1 ], [ 2, 3 ] ]

but according to the reamde it should result in

[ [ 0, 1 ], [ 0, 2 ], [ 1, 3 ], [ 2, 3 ] ]

The problem seems to be that the module expects the cells to be oriented the same. This, however isn't the case in the example, but it is also nowhere noted that the library expects this. If one fixes the orientation in the input (using e.g. var cells = [[0,1,2], [3,2,1]];), the expected result shows up.

Duplicate faces in bounday of adjacent tetrahedrons

If I understood the purpose of this module correctly, the simplical complex boundary of two adjacent tetrahedrons (one shared face) should be their "outer" surface, i.e. the inner shared face would not be part of the result triangle set. If this is correct, it is not working as expected. Below I try to construct the boundary of two adjacent tetrahedrons, sharing triangle [2,3,1]:

bnd([[2, 3, 1, 4], [3, 1, 0, 2]]]

This results in

[[1, 0, 2], [3, 1, 0], [0, 2, 3], [2, 3, 1], [2, 3, 1], [1, 4, 2], [3, 1, 4], [4, 2, 3]]

But I think should result in (shared face [2, 3, 1] removed):

[[1, 0, 2], [3, 1, 0], [0, 2, 3], [1, 4, 2], [3, 1, 4], [4, 2, 3]]